1. Field of the Invention
The present invention relates to radiation detectors. More particularly, the present invention relates to a system and method for correcting parallax error in a detector resulting from inaccurately assessing where the photon interacted with the detector, and thereby increasing efficiencies of traditional Positron Emission Tomography (PET) devices on a photons per unit of radiation basis.
2. Description of Related Art
These devices (detectors) are about 200 times smaller than the large detectors for high-energy physics and require identification of only one particle, the photon. The task to be solved of capturing and identifying the particles is relatively easier than before: one particle instead of five on a detector 200 times smaller.
The use of positron emissions for medical imaging has been well document from the early 1950's, see “A History of Positron Imagining,” Brownell, Gordon, presented on Oct. 15, 1999, Massachusetts General Hospital, which is incorporated herein by reference in its entity. PET imaging has advantages over other types of imaging procedures. Generally, PET scanning provides a procedure for imaging the chemical functionality of bodily organs rather than imaging only their physical structure, as is commonly available with other types of imaging procedures such as X-ray, Computerized Tomography (CT), or Magnetic resonance imaging (MRI). PET scanned images allow a physician to examine the functionality heart, brain, and other organs as well as diagnosing disease groups which cause changes in the cells of a body organ or in the manner they grow, change, and/or multiply out of control, such as cancers.
Positron Emission Tomography (PET) is a medical imaging technique that involves injecting a natural compound, such as sugar or water, labeled with a radioactive isotope into a patient's body to reveal internal biological processes. As the isotope (positron) circulates within the patient's body. The positron annihilates with and electron and emits pairs of photons in diametrically opposed directions (back-to-back). A PET device is made of a set of detectors coupled to thousands of sensors that surround the human body. These detectors (crystals) capture the photons emitted by the isotope from within the patient's body at a total rate of up to hundreds of millions per second, while the sensors (transducers such as PMTs) convert them to electrical signals, and send the signals to the electronics.
Other applications for detecting particles (photons, electrons, hadron, muon and jets) are well known, such as with regard to experiments in high energy physics. While particle detection in high energy physics and medical imaging have some common ground, differences between the disciplines exist. One distinction between the usages is that the detectors used in medical imaging are approximately 200 times smaller than the larger detectors employed in high-energy physics applications. Moreover medical imaging PET applications require the identification of only a single type of particle, the photon.
Typically, prior art Positron Emission Tomography (PET) devices require the injection into the patient's body of a radiation dose that is 10 to 20 times the maximum radiation dose recommended by the International Commission on Radiological Protection (ICRP). This amount is necessary because, at best, prior art PET devices only detect 2 photons out of 10,000 emitted in the patients' body. Currently the largest manufacturers of PET (General Electric Company and Siemens AG (ADR)) which command in excess of 90% of the world market, are manufacturing two different PET (PET/CT) systems with very similar performance and are selling them at very similar prices. However, although the price and performance of the systems from the different manufactures are comparable, one manufacturer's system (Siemens) uses nearly ideal crystal detectors, while contrastingly, the other manufacturer's system (General Electric) uses cheaper, lower quality crystal detectors with slower decay time. Consequently, the manufacturer using the cheaper, lower cost detectors, expend on the order of only 10% the price of the ideal crystals used in their competitor's systems. Thus, the question arises: how it could be that even though one manufacturer uses crystals detectors that are ten times more expensive that the other manufacturer, the price and performance of the two PET systems from the different manufacturers are very comparable.
Anecdotally, the present inventor has analyzed the progress of the most significant PET improvements made in the most recent 17 years, see “400+ times improved PET efficiency for lower-dose radiation, lower-cost cancer screening,” 3D-Computing, Jun. 30, 20010, ISBN: 0970289707, which is incorporated herein by reference in its entity. During that time period the efficiency of PET improved at a rate of between two and three times every five years. The analysis included technical literature, patents (including those assigned to GE and Siemens) and also PETs that were built as prototypes at several universities but were never commercialized. At the current improvement rate of PET advancement, conservatively it would take several decades of improvements for the radiation dose necessary for a PET procedure to come within the maximum radiation dose recommended by the ICRP.
What is needed is a means for increasing the accuracy and efficiencies of PET devices, enabling caregivers to more accurately diagnose ailments related to the functionality of body organs and not just inferences from the structure of the organs. Additionally, what is needed is a quantum advance forward in PET devices and procedures wherein patients can receive the benefits of PET imaging without the associative risks from the radioactive doses necessary for the procedures. Finally, what is needed is a means for reducing the associated risks and increasing detection efficiencies associated with PET imaging procedures to such an extent that the benefits of PET imaging can be applied in well body care and preventative medicine strategies for apparently healthy individuals; as a standard health assessment and diagnostic tool for regular, periodic checkups.